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JOURNAL OF THE EXPERIMENTAL ANALYSIS OF BEHAVIOR

1975, 23, 199-206

NUMBER

2

(mARcH)

KEY PECKING IN PIGEONS PRODUCED BY PAIRING KEYLIGHT WITH INACCESSIBLE GRAIN' THOMAS R. ZENTALL AND DAVID E. HOGAN UNIVERSITY OF PITTSBURGH In Experiment I, keylight was paired with inaccessible grain delivery (under two conditions of keylight intensity) to determine if autoshaping would occur in the absence of primary reinforcement. In Experiment II, the procedure was repeated with accessible grain, for comparison. In Experiment III, the procedures were repeated with explicitly unpaired presentations of keylight and either inaccessible or accessible grain. The results indicated that key pecking occurred as quickly in the presence of keylight pairings with inaccessible grain as with accessible grain, though (except for one bird) key pecking was not maintained with inaccessible grain. Furthermore, compared to the dim keylight, the bright keylight greatly suppressed key pecking when paired with inaccessible grain, and reduced the rate of key pecking when paired with accessible grain. Little key pecking occurred in groups exposed to explicitly unpaired presentations of keylight (whether bright or dim) and grain (whether accessible or inaccessible). When the birds in Experiment III were retested with explicitly paired presentations of keylight and grain, little key pecking was observed, suggesting suppressive effects of prior explicitly unpaired presentations. It is suggested that the effects of key-brightness manipulation were produced by the association of grain with cues other than the response key, or by distraction produced by partial illumination of the grain hopper.

eliminate responding indicates the strength of the stimulus-reinforcer association. Wessells (1974) eliminated approaches toward the key by omitting reinforcement when approaches toward the lighted key occurred, but eight to 13 sessions (40 trials each) were required to eliminate the response, and in spite of elimination of approach responses toward the key, orientation to the key persisted on all trials. Hursh, Navarick, and Fantino (1974) also reported elimination of key pecking with an omission procedure, though this finding was inconsistent and was apparently related to certain physical aspects of the operant box, (i.e., black walls and no house illumination). Hursh et al. (1974) concluded that when responding under omission procedures does occur ". . . it is probably maintained by the reinforcing effectiveness of response-dependent offset of the keylight." According to this argument (also proposed by Herrnstein and Loveland, 1972), "This research was supported in part by Biomedical keylight offset becomes a conditioned reinSciences Support Grant FR7084 from the National In- forcer due to its pairing with food. Maintained stitutes of Health to the University of Pittsburgh, and responding under omission procedures presumby Grants MH19757 and MH24092 from the National ably occurs because on trials without a reInstitute of Mental Health to the first author. Reprints sponse, keylight offset becomes associated with may be obtained from T. R. Zentall, Department of Psychology, Faculty of Arts and Sciences, University of food, and the consequence of responding is keylight offset, a conditioned reinforcer. Hursh Pittsburgh, Pittsburgh, Pennsylvania 15260. 199

Brown and Jenkins (1968) found that key pecking in pigeons could be produced by the repeated temporal pairing of a lighted response key and grain, a phenomenon they called autoshaping. They also found that key pecking would continue even if these responses had no effect on grain delivery. Since then, attempts have been made to determine further the conditions under which autoshaping would occur and be maintained. Williams and Williams (1969), for example, found that key pecking would often continue even if it prevented grain from being delivered (omission procedure). The omission procedure pits operant procedures (reinforcement contingent upon not responding) against respondent procedures (stimulus-reinforcer pairings). While key pecking was substantially reduced, the fact that the omission procedure did not

200

THOMAS R. ZENTALL and DAVID E. HOGAN

et al. (1974) suggested that the immediate occurrence of a conditioned reinforcer may be preferred over the delayed occurrence of primary reinforcement. Ingenious as the above explanation may be, it does not account for findings, similar to those of Williams and Williams (1969), that have used variations of the omission procedure. Schwartz (1972) found that neither keylight-offset/food pairings (which presumably establish keylight offset as a conditioned reinforcer) nor response-produced keylight offset (which presumably maintains responding) are necessary to produce maintained responding with the omission pro-

cedure.2 While it is doubtful that autoshaping can be explained by conditioned reinforcement, a conditioned reinforcer can be used to obtain key pecking in the absence of primary reinforcement. Patterson and Winokur (1973) reported that two pigeons given tone-grain pairings, pecked at a red response key that changed from green to red 5 sec before the tone was presented. Virtually no pecks occurred to the tone during tone-grain pairings, thus the new response occurred in the absence of primary reinforcement. Unfortunately, once responding began, noncontingent red-tone pairings were discontinued and replaced by response-contingent tone presentation in the presence of the red key, on an Fl 5-sec schedule. The change in procedure might account for the observed sharp reduction in response rate over time. Responding to the red key recovered, however, when tone-grain pairings were interspersed among red- and green-key trials, with responses to the red key reinforced with tone presentation on an Fl 1-min schedule. The first experiment of the present study sought to determine if a more direct conditioned appetitive reinforcer, the sight of grain and sound of the grain magazine, could be used to obtain key pecking in magazine-trained pigeons when keylight is followed by inaccessible grain presentation, and whether responding would be maintained under these conditions. In addition, intensity of key illumination was also manipulated with the idea that

salience of the key might affect the probability of key pecking.

EXPERIMENT Ia METHOD

Subjects Ten experimentally naive female White Carneaux pigeons, approximately 1 yr old, were maintained at 75 to 80% of their freefeeding weights. Apparatus Two pigeon test chambers were used. The intelligence panels and depth of the boxes was 17.0 cm, the width of the boxes was 28.1 cm, and height was 32.8 cm. The grain hopper (midline 12.7 cm above the floor), response key (midline 25.4 cm above the floor), and houselight (midline 31.1 cm above the floor) were all located on the vertical centerline of the intelligence panels. The two boxes were the same except for the intensity of the keylight (incandescent source), which was 0.26 m-cd in the dim-key box and 4.18 m-cd in the bright-key box as measured at the surface of the key by a United Technology Opto-meter (model 40A) with diffuser and photometric filter. The brightness of the jewelled houselight was 0.036 m-cd as measured 25 cm away. The grain magazine contained mixed pigeon grain (Purina). Procedure

Five birds were randomly assigned to each of the boxes: Subjects 1 to 5 to the bright-key box, Subjects 6 to 10 to the dim-key box. Magazine training occurred on Day 1 and involved placing the pigeon in the operant box with the magazine raised and the magazine light on. Once the bird started to eat, the magazine was lowered and then repeatedly raised (for 4 sec) and lowered at random intervals until 10 consecutive food approaches occurred. On Day 2, each pigeon was exposed to presentations of 8 sec of keylight followed by 4 sec of inaccessible grain (a transparent piece of Plexiglas placed in the hopper over the grain preventing access to grain in the raised maga2In a study presented at the 1973 meeting of the zine). The first phase of training consisted of American Psychological Association, Wasserman re- 300 such presentations (trials) separated by ported that response-produced keylight offset is unnecessary for the establishment and maintenance of key variable duration (mean 30 sec) intertrial inpecking in pigeons exposed to an omission procedure. tervals (ITIs). Key pecks were recorded but

A UTOSHAPING WITH INACCESSIBLE GRAIN had no effect on the sequence or duration of events. At the end of Phase I, the bird was removed from the box, the hopper barrier was removed, the bird was returned to the box, and Phase II began immediately. Phase II consisted of 200 trials, similar to those of Phase I, but with grain accessible when the magazine was raised. In addition, key pecks immediately terminated keylight and grain presentation. During both phases of training, the houselight was continuously on. RESULTS AND DISCUSSION Six of the 10 birds pecked at the lighted key during Phase I: all five birds in the dim-key box (Subjects 6 to 10), but only one of the birds in the bright-key box (Subject 5). The trial of the first peck, total number of responses, and number of trials with peck(s) for each bird are presented in Table 1. The same six and one additional bird (Subject 3) responded during Phase II. Trial of the first response is presented in Table 1. Table 1 Response measures for each subject in Experiments Ia and lb. Subjects were exposed to 300 pairings of keylight and inaccessible grain, followed immediately by 200 pairings of keylight with accessible grain. I Inaccessible Grain

Bird

Experiment Ia Bright key

Dim key

Trial Trials Grain First Total with Trial Peck Pecks Peck First Peck

1

-

0

0

2

-

0

0

-

3 4 5

252 5 50 20 44

0 0

0 0 5

37 -

6

7 8 9 10

Experiment Ib Dim key 11 12 13 14 15

*Dim-key

I

Accessible

27 3 6 8

7 22 5 14 41 22

12 3 6 28

58 11 16 3 917 1 10.9 20

27 5 7 3 208

17

61 2 3 5 5 5

5 46 1

26 29 1 2 X 19.4 10.9 31.6 5 Median* 14 9.5 data from Experiments Ia and lb combined.

201

The results indicate a clear effect of manipulated brightness and further suggest that pigeons will peck at a keylight paired with inaccessible grain if tested under the right conditions. While the number of key pecks made during Phase I was generally small (median = 22), compared to the number of pecks one observes when grain is accessible (see, for example, Brown and Jenkins, 1968), trial-ofthe-first-peck data are comparable to scores obtained with accessible grain (median = 27). Keylight pairings with inaccessible grain during Phase I also appeared to affect Phase II, for responding began again almost immediately when grain was made accessible (median trials to first peck in Phase II = 5). The data indicate that access to grain is not a necessary condition for initiating key pecking, though it may be necessary to maintain it. The nominal difference between the two operant boxes was the intensity of the keylight. Experiment lb attempted to ascertain whether, in fact, differential key brightness was responsible for differential key pecking. EXPERIMENT Ib To determine if the brighter key was responsible for the low probability of key pecking in that box, new birds were tested in the bright-key box with the key brightness reduced to that of the dim-key box. METHOD

Subjects Five experimentally naive female White Carneaux pigeons approximately 1-yr old (Subjects 11 to 15) were maintained at 75 to 80% of their free-feeding weights.

Apparatus and Procedure The apparatus was the same as that used in Experiment Ia, with the brightness of the keylight in the bright-key box reduced to 0.26 m-cd. The procedure was the same as that used in Experiment Ia. "In an independently performed study presented at the 1973 meeting of the American Psychological Association, Browne and Karpicke reported similar results. Forward pairings of keylight with inaccessible grain resulted in some key pecking by all five pigeons exposed to that condition, and when grain was subsequently made accessible, all birds began key pecking almost immediately.

202

THOMAS R. ZENTALL and DAVID E. HOGAN

RESULTS AND DISCUSSION All five birds tested in bright-key box with the dim keylight pecked in both Phases I and II. The trial of the first peck, total number of responses, and number of trials with peck(s) for each bird are presented in Table 1, for both Phases I and II. Again, responding occurred early (median trial to first response = 6) but (except Subject 15) was not maintained (median responses = 16). For birds in the dim-keylight condition in Experiments Ia and Ib, the distribution of responses over trial blocks plotted cumulatively is presented in Figure 1. The figure shows that all birds but Subject 15 had stopped responding by the end of Phase I. Thus, recovery of responding early in Phase II is attributable to the accessibility of grain, rather than to a carryover of Phase I responding. Persistent responding by Subject 15, but not by the other birds exposed to inaccessible grain, cannot be explained. Performance by Subject 15 is more typical of performance by birds exposed to accessible grain. By what mechanism does the bright key prevent autoshaping? Intuitively, the brighter keylight should better elicit orienting responses, which in turn should facilitate the association between the keylight and grain. But perhaps the facilitated association was between some other cue and grain. Observations of the operant boxes while the birds were being tested indicated that the onset of the bright key significantly increased the overall brightness of the box, making additional cues visible. If so, any of the new cues could have become associated with the reinforcer, rather than the key. Supportive evidence for such speculation comes from the fact that a number of brightkey birds but none of the dim-key birds were observed to peck the floor or side of the box when the keylight came on. Unfortunately, no systematic data were taken. Wasserman (1973) proposed an explanation similar to the one above to account for the fact that an autoshaping procedure produced virtually no pecking in a box without house illumination. According to Wasserman (1973), the onset of keylight in a dark box produced many cues, any of which may have been associated with the reinforcer. In the well-illuminated box, onset of the keylight produced few extra cues, and thus the lighted key became associated

with the reinforcer. Similar effects of house illumination on autoshaping have been noted by Griffin and Rashotte (1973). Alternatively, in the present experiment, it is possible that the bright keylight partially illuminated the grain hopper, which in turn acted as a distracting stimulus. Wasserman and McCracken (1974) recently found that simultaneous onset of keylight and feeder light, before grain delivery, resulted in virtually no key pecking. If the bright keylight provided "extra" cues or added significantly to the ambient light in the grain hopper, thus competing with the keylight as a cue, then one should be able to observe a similar key-brightness effect in birds exposed to more traditional autoshaping procedures, i.e., with accessible grain.

EXPERIMENT II METHOD

Subjects Ten experimentally naive female White Carneaux pigeons, approximately 1-yr old, were maintained at 75 to 80% of their freefeeding weights. Apparatus and Procedure The apparatus was the same as that used in Experiment I, with a dim keylight (0.26 m-cd) in one box and a bright keylight (4.18 m-cd) in the other. The procedure was the same as that used in Experiment I, Phase I, except that grain was accessible on all trials, and the experiment was terminated after 300 trials. Five birds were randomly assigned to each of the boxes: Subjects 16 to 20 to the bright key box, Subjects 21 to 25 to the dim-key box. RESULTS AND DISCUSSION The data from Experiment II are presented in Table 2. All birds pecked at the lighted key. A difference in the expected direction between the bright and dim conditions was found for trials to the first peck, Mann-Whitney U(5,5) = 4, p = 0.048, total number of pecks, U(5,5) = 6, p = 0.111, and number of trials with peck(s), U(5,5) = 5, p = 0.075. Apparently, when grain is accessible, the bright keylight partially suppresses but does not prevent

pecking.

A UTOSHAPING WITH INACCESSIBLE GRAIN

203

Table 2 Response measures for each subject in Experiment II. Subjects were exposed to 300 pairings of keylight with accessible grain.

900gF 15

Accessible Grain Trial First Peck

600 Bird Bright key

a)

17

Median 21

23 208 86.0 80 46

22 23

27 5

24

13

X Dim key

0

3

6

9

60

15

12

°11

'~~~-

E C..,

102 80

17 18 19 20

o Qn 300 a) C)

16

7

25 X

£9

40 .

20

*6 10 Y 13

£8

a 12 0

,,,,,,,,, ..

3

6

9

12

7 °t~w14

15

Blocks of 20 Trials Fig. 1. Cumulative responses in blocks of 20 trials for birds exposed to a dim key paired with inaccessible grain (Experiments Ia and Ib).

Comparison of the data from dim-key birds in Experiments I and II indicates that while median total responses differ greatly (555 with accessible grain; 19 with inaccessible grain), the median trial of the first peck is virtually the same for both groups (13 with accessible grain, 14 with inaccessible grain). Thus, pairings of a dim keylight with inaccessible grain produced pecking in pigeons as rapidly as pairings of the same keylight with accessible grain. The maintenance of key pecking, however, required keylight pairings with accessible grain. Thus, Patterson and Winokur's (1973) failure to observe maintained key pecking, when color change was paired with a conditioned reinforcer, may not have been due to the change in procedure (once responding had begun) from autoshaping to responsecontingent tone presentation.

Median

19.6 13

Total Trials Pecks with Peck

43 149 1000 1904 11 621.4 149 246 161 2027 555 4127 1423.2 555

35 81 171 224 4 103.0 81 131 103 289 214 294 206.2 214

EXPERIMENT III Though trial-of-the-first-peck data from Experiment I, dim-key condition, compare favorably with autoshaping data from other experiments, Hitzing and Safar (1970) found that prior exposure to keylight-only trials, followed by magazine training, was sufficient to produce key pecking in nine of 12 birds, within 16 subsequent presentations of keylight-only trials. Thus, it is possible that forward pairings of keylight with grain were not responsible for key pecking in Experiment I, especially since responding was not maintained. If responding in Experiment I was not due to keylight-grain pairings, then birds presented with keylight and grain with keylight signalling the absence of grain (explicitly unpaired) should perform as did the birds in Experiment I. Experiment III involved a 2-by-2 design with bright-dim keylights and inaccessible-accessible grain as the two variables manipulated. All birds given inaccessible grain were then given accessible grain as in Experiments I and II. Finally, all birds were given forward pairings of keylight and grain to assess the effects of explicitly unpaired trials on subsequent explicitly paired trials. METHOD Subjects Twenty experimentally naive female White Carneaux pigeons, approximatetly 1-yr old,

204

THOMAS R. ZENTALL and DAVID E. HOGAN

were maintained at 75 to 80% of their freefeeding weights. Apparatus and Procedure The apparatus was the same as that used in the first two experiments. All birds were magazine trained as described in Experiment Ia. On Day 2, all birds were exposed to explicitly unpaired presentations of keylight (8 sec) and grain (4 sec) such that grain presentation could not follow keylight by less than 15 sec. Grain presentations were arranged on a variableduration (mean 15 sec) tape that started running 15 sec after keylight presentations and stopped with the next keylight presentation. The time between keylight presentations was of variable duration with a mean of 30 sec. For half the birds (Subjects 26 to 35), the grain was inaccessible as it was in Experiment I; for the remaining birds (Subjects 36 to 45), the grain was accessible as it was in Experiment II. Half the birds in each group (Subjects 26 to 30 and 36 to 40) were presented with a bright key (4.18 m-cd) while the remaining birds (Subjects 31 to 35 and 41 to 45) were presented with a dim key (0.26 m-cd). For birds receiving inaccessible grain presentations (control for Experiment I), Phase I consisted of 300 keylight presentations, after which Phase II began after the hopper barrier was removed. Phase II consisted of 200 keylight presentations explicitly unpaired with accessible grain presentations, but unlike the procedure of Experiment I, pecks on the lighted key were not reinforced and did not terminate the keylight. Birds receiving accessible grain presentations (control for Experiment II) re-

in Table 3. In general, little responding was observed for birds exposed to explicitly unpaired presentations of keylight and grain, regardless of accessibility of grain or brightness of key. Inaccessible Grain Comparison of birds exposed to inaccessible grain presentations with similarly treated birds from Experiment I, suggests that pecking the dim key in Experiment I was largely due to the forward pairings of keylight and inaccessible grain (a conditioned reinforcer). Birds exposed to explicitly paired presentations of dim keylight with inaccessible grain, responded more, Mann-Whitney U(5,10) = 3, p < 0.01, responded earlier, U(5,10) = 4, p